Update, have not heard back from St Cynwyd church yet, but Glamorgan Archive confirmed Thomas, Hannah and son Richard Thomas (formerly foster son Richard Found from 1851 census) are buried in same grave and they think it is in the new graveyard, but the grave plan for the new churchyard in the Archive is in poor condition and dated 1864, so prior to burials in my case. The Archives also checked the Glamorgan Family Historical Society's Monumental Index for the church and came up with the memorial inscription and translated it for me. All very helpful.
I'm going to ask the Archives and/or Vicar if they can enlighten me further on burial in the Parish church if the Thomases were members of an independent church/chapel.
Question: how can i research adoption of Richard Found into the Thomas family? He's not in my direct line, but I"m curious.